Round scar on my left leg that won't go away?

Scar. You should see a clinician to examine this 'scar' you need make sure that this is not a cancerous lesion.
Needs to be seen. Wounds or scars like you are describing need to be seen in order to be properly evaluated. I would suggest going to see your family doc or a dermatologist for this. They should be able to help you or point you to folks who can.